3GPP (3rd Generation Partnership Projects) defines a service called “MBMS” (Multimedia Broadcast Multicast Service) (Non Patent Literature 1˜7).
MBMS is a service that simultaneously transmits, by broadcasting or multicasting, multimedia data (hereinafter referred to as “MBMS data”) such as video and music to a plurality of UEs (User Equipment: mobile station).
Furthermore, 3GPP defines a scheme called “MBSFN (Multicast Broadcast Single Frequency Network)” as the scheme for providing MBMS.
MBSFN is a scheme for transmitting the same MBMS data to UEs in a plurality of cells formed by a plurality of Nodes B (base stations) using the same frequency and at the same timing.
Thus, when viewed from UEs, a plurality of cells can be regarded as one large communication area. This communication area is called “MBSFN cluster” and the UEs can receive MBMS data with a large gain under the control of the MBSFN cluster.
The plurality of cells that form the MBSFN cluster use not only the same frequency but also the same scrambling code, channelisation code and slot format or the like. In the present specification, the frequency, scrambling code, channelisation code and slot format are generically called “radio resources.” To be more specific, these radio resources are used for S-CCPCH (Secondary Common Control Physical Channel) which is a common physical channel used to wirelessly transmit MBMS data from a Node B to a UE in each cell.
FIG. 1 illustrates an example of configuration of a mobile communication system of W-CDMA (Wideband-Code Division Multiple Access) that provides MBMS using an MBSFN (Non Patent Literature 1).
As shown in FIG. 1, the related mobile communication system includes BM-SC (Broadcast Multicast-Service Center) 100, GGSN (Gateway GPRS Support Node, GPRS=General Packet Radio Service) 200, SGSN (Serving GPRS Support Node) 300, RNC (Radio Network Controller: control station) 400, Node B (NB) 500 and UE 800.
FIG. 1 shows two RNCs 400-1 and 400-2 as RNC 400.
Furthermore, though not shown in the figure, BM-SC 100, GGSN 200 and SGSN 300 are arranged in a CN (Core Network) and RNC 400 and Node B500 are arranged in RAN (Radio Access Network) 450 which will be described later. RAN 450 generally has a configuration in which a plurality of Nodes B 500 are connected to one RNC 400.
BM-SC 100 is a node provided with a function of authenticating a user of UE 800 to which MBMS data is transmitted, a function of managing MBMS data and a function of scheduling distribution of MBMS data or the like. Details of these operations are defined in 3GPP and are commonly known, and therefore descriptions thereof will be omitted.
GGSN 200 is a gateway node provided with a function of transferring an IP (Internet Protocol) packet (message and MBMS data integrated into an IP packet) sent from BM-SC 100 to SGSN 300 and a function of transferring the IP packet sent from SGSN 300 to BM-SC 100 or the like. Since details of these operations are defined in 3GPP and are commonly known, descriptions thereof will be omitted.
SGSN 300 is a node provided with a function of routing/transferring an IP packet, a function of performing mobility management and session management necessary for mobile communication or the like. Since details of these operations are defined in 3GPP and are commonly known, descriptions thereof will be omitted.
RNCs 400-1 and 400-2 are nodes provided with a function of controlling RAN 450. For example, RNCs 400-1 and 400-2 determine radio resources of S-CCPCH in cells 600 under their control, instruct Node B 500 to set the S-CCPCH, determine transmission timing for transmitting MBMS data in cell 600 under their control and transmit MBMS data to each Node B 500 in synchronization with the transmission timing. Since details of these operations are defined in 3GPP and are commonly known, descriptions thereof will be omitted. Assume that “under control” in the present specification refers to subordinate nodes connected to the own node, cells formed by the subordinate nodes, MBSFN clusters or the like.
Thus, RNCs 400-1 and 400-2 independently determine radio resources and transmission timing in cells 600 under their control.
Thus, MBSFN cluster 700-1 under the control of RNC 400-1 and MBSFN cluster 700-2 under the control of RNC 400-2 are formed respectively.
Node B 500 is a node provided with a function of setting radio resources in an S-CCPCH based on instructions from RNCs 400-1 and 400-2 and a function of converting MBMS data sent from RNCs 400-1 and 400-2 to radio data and transmitting the radio data to UE 800 in cell 600 through the S-CCPCH. Since details of these operations are defined in 3GPP and are commonly known, descriptions thereof will be omitted.
Here, with reference to FIG. 2, gains of UE 800 when MBSFN is used will be described in comparison with gains when MBSFN is not used. In FIG. 2, (a) shows frequency utilization efficiency of UE 800 when MBSFN is used, disclosed in Table 7 of Non Patent Literature 2 and (b) shows frequency utilization efficiency of UE 800 when MBSFN is not used, disclosed in Table 8 of Non Patent Literature 2.
First, a case will be described as an example where UE 800 is a Type-3 receiver and has a configuration of combining signals received through three radio links (receiver capable of equalizing 3RLs, RL=Radio Link). In this case, the frequency utilization efficiency is 0.602 [b/s/Hz] when MBSFN is used, whereas the frequency utilization efficiency is as low as 0.4736 [b/s/Hz] when MBSFN is not used. On the other hand, when there are seven radio links, the frequency utilization efficiency is 1.075 [b/s/Hz] when MBSFN is used, which is significantly different from 0.4736 [b/s/Hz] when MBSFN is not used.
It is obvious from this result that gains of UE 800 are very small when MBSFN is not used.